Lecture 9-Local Potentials Flashcards
How does the size of a fiber affect resistance?
larger fiber= decreased resistance
What does the length constant (lambda) represent?
How FAR a signal will travel before it dissipates (ratio of the membrane resistance/internal restance)
How does an increase in membrane resistance affect the number of membrane channels?
increased resistance= less channels
How does a decrease in membrane resistance affect the number of membrane channels?
decreased resistance= more membrane channels (membrane is more leaky)
How does increasing the membrane resistance affect the time constant?
increased membrane resistance= increased time constant
How is the resistance of the membrane affected by opening membrane channels?
more open channels= decreases membrane resistance
How does myelin affect the membrane resistance and time constant?
myelin increases the membrane resistance and time and length constant
How many length constants does it take for a signal to dissipate?
5 length constants
How could you increase the length constant?
increase membrane resistance (less holes) or increase internal resistance (large fiber diameter)
Why do we ignore the external resistance when calculating the length constant?
because volume of extracellular fluid is so large the resistance is very close to zero
What does a larger capacitance mean?
you need more voltage to “charge up” the membrane
What does the time constant represent?
How long it take to charge the membrane (think of the hose example)
How does the resistance of the membrane affect the time it takes to charge the membrane (time constant)?
increased resistance= increases time constant (slower signal-good for slow discharge, allows for summation of signals)
decreased resistance= decreases time constant (faster signal-good for quick response)
How is a local potential difference from an action potential?
has no threshold and therefore can be graded by amplitude
declines with distance
How many time constants are require to reach the full charge value?
5 time constants
What controls the time course by which a local potential rises and decays?
resistance and capacitance
What does increasing the internal resistance do to the length constant?
an increased internal resistance results in a decreased length constant
How are nerve fibers classified?
based on diameter of fiber and degree of myelination
What classification of nerve fibers includes the slowest fibers that are either unmyelinated or have very little myelin?
c fibers
What classification of nerve fibers contains the largest, heavily myelinated nerve fibers?
A alpha fibers
What is Guillan Barre Syndrome?
autoimmune disease that affects the Schwann cells, causing demyelination in the PNS and decreased conduction velocity
What does multiple sclerosis cause?
demylelination in the CNS (attack of oligodendrocytes)
